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What is the purpose of the stomach?
The stomach initiates digestion of food.
Describe the gastric mucosa.
- Simple columnar epithelium
- Gastric glands are found in the depressions of the epithelium
- Apical/lumenal spithelial secretions are mucous, acid, and proteases
- Basal secretions are hormones and paracrine factors
Transient gastric mucosal folds
How many sphincters are in the stomach and where are they located?
- Lower Esophageal/Cardiac Sphincter
- Pyloric Sphincter
What are the six type of cells in the gastric epithelium?
- surface lining cell
- regenerative cell
- mucous neck cell
- oxyntic (parietal cell)
- zymogenic (chief) cell
- enteroendocrine cell
What is the function of chief cells?
- Secrete zymogens apically into the lumen
- Zymogens are activated by acid hydrolysis
What is the function of enteroendocrine cells?
- Secrete hormones and paracrine factors
- ie. Vasoactive Intestinal Peptide (VIP) - increases peristalsis of intestines
- Gastrin - increases parietal cell acid secretion in stomach and relaxes pyloric sphincter
What is the function of the small intestine?
- Digestive- via enzymes delivered to the small intestine from the pancreas
- Absorptive - via mucosa
Describe the layers of the small intestine.
- Epithelium - simple columnar, absorptive cells (Enterocytes), protective mucous secreting goblet cells, anti-bacterial paneth cells
- Lamina Propria - Loose connective tissue, many vascular capillaries and lymphatic capillaries (central lacteals), prominent MALT
- Submucosa - alkaline, mucous secreting 'Brunner's Glands'
How does the small intestine increase its absorptive surface area?
- Makes use of microvilli (projections) and crypts/glands (depressions)
- Microvilli contain many channels/transporters in plasma membranes
What are paneth cells?
- Contain apical pink/eosinophilic granules
- Secrete antibacterial lysosymes
- Can become phagocytic, antigen-presenting cells
What are Brunner's Glands?
- Exocrine, secretory glands found in the submucosa all the way to the muscularis mucosa
- Secrete protective, alkaline mucous which is protective of acid produced by the stomach
- Ducts empty into base of intestinal crypts
Describe the MALT in the small intestine.
- B and T Cell aggregates (no CT capsule)
- Can be activated by Paneth cell-mediated Antigen Presentation
- Pale germinal centers indicate B Cell Activation
- Increase in numbers towards the terminal end of the small intestine
- In appendix (at small/large intestinal junction, fill entire lamina propria)
Describe the layers of the large intestine.
- Mucosa: Absorptive (especially for H2O), crypts/glands present, but no villi
- Epithelium: Simple columnar; enterocytes with high number of goblet cells
- Submucosa: no brunner's glands
- M. Externa: Terminal thickenings= Anal Sphincters, smooth muscle internally and skeletal muscle externally
Describe the junction of the terminal portion of colon with the anus.
- There is an epithelial transition between columnar epithelium and stratified squamous epithelium.
- The pectinate line is the interface between endoderm and ectoderm.
- Metaplasia can occur here as well.